The Bridges

The Bridges Of Myra Canyon

myra_stationThe Carmi Subdivision of the Kettle Valley Railway extended from Midway to Penticton, a distance of 133.7 miles. A straight line from Midway to Penticton is about 50 miles. The nature of the intervening terrain was such that the engineers locating the line for the railway had to take an extremely circuitous route in order to introduce gradients which were economically feasible for operation. Much of the railway over the chosen route was easy to build, however, a small portion, through the fingers of the area known as Myra Canyon, required extensive bridgework, tunnelling and sharp curvature.

In the period when the Carmi Subdivision was under construction, 1910 to 1914, equipment and machinery such as we know today did not exist. Horses, mules, steamshovels and hoists, black powder, hand tools and men did the work, and the capabilities of these resources determined what was to be done in the way of construction in difficult terrain. Tunnelling and heavy cuttings were avoided wherever possible, usually by introducing sharper curvature than might be desired. Watercourses and depressions were not crossed with culverts and fills but by wooden bridges, either pile or frame trestles. The theory was that the timber structures were quicker to install than filling, and could be replaced at a later date by works of more permanence when funds were available.

The Railway identifies locations by mileage on Subdivisions. The Carmi Subdivision began at Midway, Mile 0.0 and ended at Penticton , Mile 133.7, more or less. Myra Station was at mile 83.9. The first of the Myra Canyon bridges was designated 85.0 and the last, 90.4. Ruth Station was at Mileage 91.2. The section of heavy work, then, was mile 85.0 to 90.4, or 5.4 miles. In this section, in 1960, there were sixteen timber framed trestles, two steel bridges consisting of through plate girders on steel towers and two short tunnels. This is not exactly what existed at the time of original construction but will suffice for this exercise.

pooley_creekAll the bridges in the 5.4 miles of Myra Canyon were originally timber trestles, constructed largely of local Douglas Fir timber, framed and erected at the sites by highly skilled bridgemen and carpenters. The timber was untreated. The life expectancy for each bridge was about fifteen years, give or take a year or two. The bridges were subjected to rigorous inspections at regular intervals, record made, and remedial action, if necessary, was taken. Maintenance was carried out by permanent Bridge and Building crews employed by the Railway under the direction of the various foremen and the Bridge and Building Master. Maintenance usually consisted of tightening bolts, replacing broken braces and other damaged timber, and jacking and shimming the structure to correct any misalignments, usually arising from settlement.

The average life of an untreated frame trestle is about fifteen years. The Kettle Valley Division was winding down in the early seventies. Simple arithmetic then tells us that the trestles in Myra Canyon in 2003 are, with one exception, fourth generation, all built in the period 1958 to 1962. They are, then, approximately 43 years old, and, in each case, three trestles preceded each of them at each location.

water_tankOver the years, as replacement trestles were built, only minor changes in the basic design were made, however, about 1956, when a further cycle of renewals was looming, changes became necessary. The main load carrying components in the structure, the stringers, caps and posts, were cut from select structural Douglas Fir. These components are massive. Stringers are 10 inches wide, 20 inches deep and 30 feet long. Caps are 12 inches wide, 18 inches deep and up to 20 feet long. Posts are 12 inches by 12 inches and of varying lengths over 20 feet long. Timber of these dimensions and grade were becoming not only extremely expensive but often difficult to supply. Something had to be done, the result being a complete redesign of the structure. Dimensions were decreased but the number of structural members was increased, for example, stringers, formerly 10 inches by 20 inches were reduced to 9 inches by 18 inches but where six stringers were formerly used to span a 15 foot opening, now eight stringers were used. Other changes followed. However, the significant change was made from untreated timber to pressure treated timber, the treating agent in this case being creosote. The expected life for a treated framed trestle was now taken as thirty years although there was no precedent for this figure. The economic picture therefor changed favourably. For creosoted timber to live up to expectations, it is mandatory that there be no raw or untreated surfaces. Therefor, to be fully effective, each member in the structure had to be sized, framed and bored before pressure treating with creosote. This meant that staff would have to be assigned to prepare the drawings for the framing yard. Here, the effort was huge, but was carried out effectively by the engineering staff of the Kettle Valley Division at Penticton, Gordon Brockhouse and Peter Beulah specifically.

ruth_stationIt is difficult to describe the complexities involved in drawing a plan for a piece of timber to be installed in a trestle such that all jointing and bolt holes line up precisely. If the bridge was on tangent, that is, straight, and level as well, the task is at its simplest. Such was not the case for many of the bridges in Myra Canyon where curvature and ascending and descending grades are found on the trestles. This meant that each member, particularily caps, had to be framed to accommodate superelevation, or “banking” and each one would be different. There was a multitude of variables introduced requiring calculations and care in framing. Over four or five years of construction to the new design, few field corrections had to be made, a tribute to the care taken in the office and drafting room as well as the framing yard. Each timber member was matchmarked to indicate its position on plan in the trestle. The calculations for dimensional framing were done then in a way which today, perhaps, would be considered old fashioned. Computers and programs therefor were still in the future. The tools were trigonometric tables, logarithmic tables, Smoley’s tables of slopes and rises and slide rules. It was grinding, monotonous work, but important. An error in framing would result in delay, difficulty and added cost when making the correction in the field.

The replacement of an old frame trestle with a new frame trestle followed well tested methods by the bridge crews involved. A trestle had six main features. A deck of ties and stringers which rested on caps spaced at 15 foot centres. The caps were the top member of a “bent” the vertical structure which consisted of a series of “frames,” cap at the top, sill at the bottom with five or six vertical posts between. Each frame, heights of which varied from sixteen feet upwards, was called a “storey” and some trestles had as many as ten or more stories. When a new trestle was to be built to replace an old trestle, one important consideration was to do the work at the same time maintaining a smooth traffic flow. This was done principally by building the new structure within the interstices of the old and advancing the bracing as new bent after bent was installed and removing the old bents. The new deck was advanced simultaneously and closed up with temporary members from the new to the old to allow traffic to proceed.

When the aforementioned redesign of the trestles was introduced and replacement construction begun, it was apparent that the replacement construction work would have to be re-thought, as the locations of some members in the new design clashed with existing old members. However, new methods were soon worked out, thanks mainly to the bridge contractors, a firm from Vancouver Island which had considerable experience working on trestles on the Esquimalt and Nanaimo Railway. The two principals of the firm, Bun Dobson and Ken Harcus, relatively young men, took a personal interest in the work and their planning together with their highly skilled crews and appropriate machines resulted in a smooth process of trestle reconstruction over a period of four years.

Some of the reconstruction to the new design was also undertaken by railway forces. Similarily, in the earlier years, most of the work was again done by railway forces. In the early period, all the framing using untreated timber was done on the site, and bridge replacement was done, as usual, with no delays to traffic. Considerable knowledge and skill was necessary, and, above all, experience. Names come to mind. Bridge and Building Masters Jim Dobbie and John Duncan. Bridge and Building Foremen Frank Gee, Herb Olsen, and Tommy Grant. Bridgemen and Carpenters the likes of Dave Robison, Wally Yule, Ernie Stahl and Browning Hoist Operator Bill Halbauer, who not only ran the hoist, he orchestrated it. There were countless others who went before, too many to mention.

The frame trestle bridges in Myra Canyon were not unique to the Carmi Subdivision. There were many others on other Subdivisions, particularily in the Coquihalla Pass. What is unique, perhaps, about the Myra Canyon scenario is the concentration of heavy works over a distance of 5.4 miles. It is interesting to note that a straight line drawn from the rail entrance to Myra Canyon to its exit is less than a mile long.

Although the railway is long gone, here, at least, is a reminder of what planning and execution went into the creation and maintenance of a small piece of the transportation link across southern British Columbia.

Sic Transit Gloria Mundi

Source:
Kelowna Daily Courier, Sunday, Sept 21, 2003.